Intermittent TIMEOUT in /css/css-transitions/non-rendered-element-002.html

https://github.com/servo/servo/actions/runs/9178306777/job/25238825768
https://github.com/servo/servo/actions/runs/9178440926/job/25239349273

```
  ▶ TIMEOUT [expected OK] /css/css-transitions/non-rendered-element-002.html
  │   ▶ TIMEOUT [expected PASS] Transitions on ::before/::after pseudo-elements are canceled when the content property is cleared
  └   └   → Test timed out
```